Exhaust gas purifying apparatus

ABSTRACT

A throttle unit placed in an exhaust gas passage controls an opening-ratio of each of first and second valve members to control a gas-flow sectional area of the exhaust gas passage. When the temperature of a three-way catalyst is low, the throttle unit introduces the exhaust gas flow into a part of an outer-periphery of the three-way catalyst. This control can rapidly increase the temperature of the three-way catalyst from an early period of starting an internal combustion engine within a short period of time. The throttle unit increases the gas-flow sectional area of the exhaust gas passage according to increasing the temperature of the three-way catalyst. When the three-way catalyst reaches its activation temperature, the throttle unit instructs the first and second valve members to fully open. This decreases a pressure loss of the exhaust gas because the exhaust gas is supplied into the entire of the three-way catalyst.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to and claims priority from Japanese PatentApplication No. 2008-8305 filed on Jan. 17, 2008, the contents of whichare hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust gas purifying apparatususing a catalyst such as a three way catalyst capable of purifying anexhaust gas emitted from an internal combustion engine such as a dieselengine under a low temperature of the catalyst in the early period ofstarting the internal combustion engine.

2. Description of the Related Art

Internal combustion engines such as diesel engines and gasoline enginesinclude a problem of increasing the amount of specified materials suchas hydro carbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx)contained in an exhaust gas emitted from such an internal combustionengine mounted to a vehicle when the temperature of catalyst placed inan exhaust gas purifying apparatus mounted to the vehicle is low, forexample, during early period of starting the internal combustion engine.For this reason, the catalyst placed in the exhaust gas purifyingapparatus does not adequately reach its optimum temperature, namely, itsactivation temperature to activate the function of the catalyst.

In order to solve such a conventional problem, Japanese patent laid openpublication No. JP 2004-100481 has proposed an improved structure of anexhaust gas purifying apparatus. In the structure, a low pressure-losspart is formed in a central part in the diameter direction of theexhaust gas purifying apparatus. The exhaust gas is flowing easilythrough the central part of the exhaust gas purifying apparatus becausethe central part is lower in pressure than the remaining part of theexhaust gas purifying apparatus. This enables the exhaust gas to be passeasily through the exhaust gas purifying apparatus when the internalcombustion engine of the vehicle starts. Thereby, the temperature of theexhaust gas purifying apparatus is increased.

However, from the viewpoint of strength, it is in general difficult touse a usual ceramics support as the exhaust gas purifying apparatushaving the low pressure-loss part formed at the central part thereof.Still further, it is hard to concentrate the exhaust gas flow using apressure difference between the central part and the remaining part ofthe exhaust gas purifying apparatus. Still furthermore, it is necessaryto close the low pressure-loss part after the temperature of the exhaustgas, namely, of the catalyst reaches an optimum temperature such as itsactivation temperature. As described above, closing the central part ofthe exhaust gas purifying apparatus will increase the pressure loss ofthe exhaust gas to the entire of the exhaust gas purifying apparatus. Inorder to avoid that conventional problem and to keep the capability toadequately purifying the exhaust gas, it is necessary to increase thesize of the exhaust gas purifying apparatus. However, such aconventional solution will cause another problem from the viewpoint ofminiaturization.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an exhaust gaspurifying apparatus capable of rapidly increasing the temperature of acatalyst placed therein for a short period of time without increasingthe pressure loss of an exhaust gas and without increasing the size ofthe exhaust gas purifying apparatus. The catalyst such as a three waycatalyst placed in the exhaust gas purifying apparatus according to thepresent invention is capable of capturing specified materials such ashydro carbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx)contained in an exhaust gas emitted from an internal combustion enginesuch as a diesel engine and a gasoline engine. The purified exhaust gascontaining a smaller amount of those specified materials is thendischarged from the exhaust gas purifying apparatus to outside.

To achieve the above purposes, the present invention provides an exhaustgas purifying apparatus having an exhaust gas pipe, a catalyst unit, anda throttle unit. The exhaust gas pipe forms an exhaust gas passage inwhich an exhaust gas emitted from an internal combustion engine flows.The catalyst unit has a catalyst placed in the exhaust gas passage. Thecatalyst temperature detection means is capable of detecting atemperature of the catalyst placed in the catalyst unit. The throttleunit is placed in at least one of an upstream side and a downstream sidethereof. The throttle unit introduces the exhaust gas flowing in theexhaust as passage into a part of the catalyst unit when the temperatureof the catalyst detected by the catalyst temperature detection means islower than an activation temperature of the catalyst.

When observed from the flowing direction of the exhaust gas in theexhaust gas passage formed in the exhaust gas pipe, the throttle unit isplaced on at least one of the upstream side and the downstream sidethereof. The throttle unit locally introduces the exhaust gas into apart of the catalyst placed in the catalyst unit when the temperature ofthe catalyst is lower than its activation temperature. That structureallows the exhaust gas emitted from an internal combustion engine to beintroduced into the part of the catalyst when the temperature of thecatalyst is low, namely, in the early period of starting the internalcombustion engine. This allows the temperature of the part of thecatalyst to locally and rapidly rise, through which the exhaust gas isconcentrated in flow to the part of the catalyst such as the centralpart or the outer peripheral part of the catalyst. On the other hand,when the temperature of the catalyst reaches or is over its activationtemperature, the throttle unit supplies the exhaust gas into the entireof the catalyst without closing the gas-flow sectional area of theexhaust gas passage. Accordingly, without causing the pressure loss ofthe exhaust gas and without increasing the size of the exhaust gaspurifying apparatus, it is possible to rapidly increase the temperatureof the catalyst such as a three way catalyst placed in the catalyst unitwithin a short period of time after the internal combustion enginestarts or re-starts. Still further, the structure and function of theexhaust gas purifying apparatus of the present invention can efficientlyeliminate specified materials, for example, hydro carbon (HC), carbonmonoxide (CO), and nitrogen oxide (NOx) contained in the exhaust gasemitted from the internal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred, non-limiting embodiment of the present invention will bedescribed by way of example with reference to the accompanying drawings,in which:

FIG. 1A is a schematic cross section of a part of an exhaust gaspurifying apparatus according to the first embodiment of the presentinvention;

FIG. 1B is a cross section of the part of the exhaust gas purifyingapparatus according to the first embodiment along the B-B line in FIG.1A;

FIG. 2 shows a schematic diagram of a gasoline engine system (as aninternal combustion engine system) equipped with the exhaust gaspurifying apparatus according to the first embodiment of the presentinvention;

FIG. 3A to FIG. 3C, each shows an opening state of a throttle unit (or avalve) assembled into the exhaust gas purifying apparatus according tothe first embodiment of the present invention;

FIG. 4 is a flow chart of the operation flow of the exhaust gaspurifying apparatus according to the first embodiment of the presentinvention;

FIG. 5A is a diagram showing a relationship between a temperature of athree way catalyst and an elapsed period of time counted from a gasolineengine start or re-start;

FIG. 5B is a diagram showing a relationship between the elapsed periodof time counted from the gasoline engine start or re-start and aconcentration of hydro carbon (HC) contained in an exhaust gas emittedfrom engine main system, one is equipped with the exhaust gas purifyingapparatus according to the first embodiment of the present invention andthe other (as a comparison example) is equipped with a conventionalexhaust gas purifying apparatus;

FIG. 6 is a schematic cross section of a part of the exhaust gaspurifying apparatus according to the second embodiment of the presentinvention;

FIG. 7 is a schematic cross section of a part of the exhaust gaspurifying apparatus according to the third embodiment of the presentinvention;

FIG. 8 is a schematic cross section of a part of the exhaust gaspurifying apparatus according to the fourth embodiment of the presentinvention;

FIG. 9 is a schematic cross section of a part of the exhaust gaspurifying apparatus according to the fifth embodiment of the presentinvention; and

FIG. 10 is a schematic cross section of a part of the exhaust gaspurifying apparatus according to the sixth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, various embodiments of the present invention will bedescribed with reference to the accompanying drawings. In the followingdescription of the various embodiments, like reference characters ornumerals designate like or equivalent component parts throughout theseveral diagrams.

A description will be given of first to sixth embodiments of an exhaustgas purifying apparatus and an engine system equipped with the exhaustgasp purifying apparatus according to the present invention withreference to FIG. 1A to FIG. 10.

First Embodiment

FIG. 2 shows a schematic diagram of an gasoline engine system as aninternal combustion engine system equipped with an exhaust gas purifyingapparatus according to the first embodiment of the present invention. Asshown in FIG. 2, the engine system 10 has a gasoline engine 11 and anexhaust gas purifying apparatus 12. The gasoline engine 11 is comprisedof an engine main system 13, an intake air system 14, an exhaust gassystem 15, a gasoline supply system 16, and a control unit 17 (or anelectronic control unit (ECU)).

The engine main system 13 has pistons which are located in cylinders.Each piston 13 performs reciprocating motion in the correspondingcylinder. Each cylinder 18 is equipped with an injector 21 to inject afuel. The gasoline engine 18 uses gasoline as fuel. It is possible touse liquefied petroleum gas (LPG), liquefied natural gas (LNG), andalcohol such as ethanol instead of gasoline as fuel.

It is also possible for the engine system 10 to incorporate a dieselengine instead of the gasoline engine 11. Through the specification ofthe present invention, the engine system 10 is a gasoline engine system.

The injector 21 injects gasoline as fuel into a combustion chamber 22formed between the cylinder 18 and the piston 19. In the firstembodiment, the gasoline engine 11 is a direct injection type gasolineengine to inject gasoline from the injector 21 into the combustionchamber 22. However, the present invention is not limited by thisstructure. It is possible to apply the exhaust gas purifying apparatusinto a gasoline engine system of pre-mixed combustion type.

The intake air system 14 has an intake air pipe 23 that forms an intakeair passage. One end part of the intake air pipe 23 communicates withthe engine main system 13. The intake air pipe 23 is equipped with anair filter placed at the end part of the air atmosphere side thereof.After eliminating foreign materials such as dust by the air filter, theair is introduced into the engine main system 13 through the intake airpassage in the intake air pipe 23.

The air intake system 14 has a throttle 25. The throttle 25 opens andcloses the intake air passage in order to adjust the amount of theintake air flowing in the intake air passage.

An intake air valve (not shown) is placed at the end part of the intakeair passage at the combustion chamber 22 side. Opening and closing theintake air valve (not shown) permits and interrupts the air introductionfrom the intake air passage into the combustion chamber 22.

The exhaust gas system 15 has an exhaust gas pipe 26 that forms anexhaust gas passage. One end part of the exhaust gas pipe 26communicates with the engine main system 13. The exhaust gas pipe 26 hasa muffler 27 placed at the end part of the exhaust gas pipe 26 at theair atmosphere side, namely, opposing the engine main system 13 side.

The exhaust gas emitted from the engine main system 13 is discharged tothe outside atmosphere through the exhaust gas passage.

An exhaust gas valve (not shown) is placed at one end part of theexhaust gas passage at the combustion chamber 22 side. Opening andclosing the exhaust gas valve permits and interrupts the exhaust gasflow from the combustion chamber 22.

The gasoline supply system 16 is equipped with a gasoline tank 28, asupply pipe 29, a pump 31, and an injector 21. The gasoline tank 28stores gasoline. The gasoline stored in the gasoline tank 28 is injectedthrough the injector 21 into the combustion chamber 22. The supply unit29 connects the gasoline tank 28 and the injector 21. The pump 31 isplaced in the supply unit 29 which is placed between the gasoline tank28 and the injector 21.

The pump 31 sucks the gasoline stored in the gasoline tank 28, andpressurizes and supplies the gasoline into the injector 21. The injector21 injects the gasoline pumped by the pump 31 as fuel into thecombustion chamber 22.

The control unit 17 is an electronic control unit (ECU) capable ofcontrolling the entire of the engine system 10. The engine system 10comprises the gasoline engine 11 and the exhaust gas purifying apparatus12 according to the first embodiment of the present invention.

The control unit 17 comprises a microcomputer having a centralprocessing unit (CPU), a read only memory (ROM), and a random accessmemory (RAM) which are omitted from FIG. 2. The control unit 17communicates with other control units (not shown) incorporated to theengine system 10 through a vehicle local area network (or a vehicle LANfor short, not shown).

The control unit 17 generates drive signals or control signals based onthe amount of depression of the accelerator pedal of the vehicle. Thecontrol unit 17 then transfers the drive signals to the injector 21 andthe throttle 25. The control unit 17 transfers the drive signal to theinjector 21 in order to obtain an optimum opening period of time of theinjector 21, namely, to obtain an optimum injection amount of thegasoline as the fuel. The control unit 17 transfers the drive signal tothe throttle 25 in order to obtain an optimum opening ratio of thethrottle 25.

The exhaust gas purifying apparatus 12 is equipped with a three waycatalyst unit 32, a temperature sensor 33 (or a catalyst temperaturedetection means), and a throttle unit 40. In the three way catalyst unit32, a three way catalyst unit 32 is placed. The control unit 17 in theengine system 10 forms the part of the exhaust gas purifying apparatus12.

The three way catalyst unit 32, the temperature sensor 33, and thethrottle unit 40 are placed in the exhaust gas system 15.

When reaching its activation temperature, the three way catalyst in thethree way catalyst unit 32 oxidizes hydro carbon (HC) contained in theexhaust gas into water (H₂O) and carbon dioxide (CO₂). Further, thethree way catalyst oxidizes carbon monoxide (CO) contained in theexhaust gas into carbon dioxide (CO₂). Still further, the three waycatalyst reduces nitrogen oxide (NOx) contained in the exhaust gas intonitrogen (N₂).

Although the first embodiment uses such a three way catalyst, it ispossible to use other catalysts such as ammonia oxidizing catalyst, NOxselective reduction catalyst, or NOx adsorbing catalyst.

The temperature sensor 33 is placed in the exhaust gas pipe 26 in whichthe three way catalyst unit 32 is also placed. The temperature sensor 33is comprised of a temperature detection element such as a thermistor.The temperature sensor 33 outputs a detection signal corresponding tothe temperature of the three way catalyst unit 32 to the control unit17.

When receiving the detection signal transferred from the temperaturesensor 33, the control unit 17 detects the temperature of the three waycatalyst unit 32. Thus, the temperature sensor 33 and the control unit17 form a catalyst temperature detection means which is used in theclaims according to the present invention.

The present invention is not limited by the above structure to detectthe temperature of the three way catalyst unit 32 by the temperaturesensor 33 mounted to the exhaust gas pipe 26, and the three way catalystunit 32 is placed in the exhaust gas pipe 26. For example, it isacceptable to place the temperature sensor 33 in the exhaust gas pipe26, which forms the exhaust gas passage, in order to detect thetemperature of the three way catalyst unit 32 based on the detectedtemperature of the exhaust gas. Still further, it is also acceptable toindirectly detect the temperature of the three way catalyst unit 32based on the temperature of a cooling water for the engine main system13.

It is possible to indirectly detect or estimate the temperature of thethree way catalyst unit 32 based on the injection amount of gasolinefrom the injector 21 or based on a correlation between the injectionamount of gasoline and the temperature of the exhaust gas.

FIG. 1A is a schematic cross section of a part of the exhaust gaspurifying apparatus according to the first embodiment of the presentinvention. FIG. 1B is a cross section of the part of the exhaust gaspurifying apparatus according to the first embodiment along the B-B linein FIG. 1A.

As shown in FIG. 1, the throttle unit 40 is placed at the upstream sideof the exhaust gas flowing in the exhaust gas passage 41 which is formedin the exhaust gas pipe 26. The throttle unit 40 has rotary shafts 42and 43 which penetrate through the exhaust gas pipe 26 in which theexhaust gas passage 41 is formed.

The rotary shafts 42 and 43 penetrate the exhaust gas pipe 26 toward thediameter direction thereof, and further toward the vertical direction ofthe central axis of the exhaust gas passage 41.

The rotary shafts 42 and 43 form coaxial shafts of a double structure.One rotary shaft 42 and a first valve member 44 are assembled together.The first valve member 44 rotates around the rotary shaft 42. The firstvalve member 44 opens and closes the exhaust gas passage 41 in theexhaust gas pipe 26 at the engine main body 13 side, opposing to theexhaust gas passage 41 at the three way catalyst unit 32 side.

The first valve member 44 rotates from a first state to a second state,where in the first state, the outer peripheral part 45 of the firstvalve member 44 is in contacts with the inner wall 46 of the exhaust gaspipe 26 around the rotary shaft 42, and in the second state, the outerperipheral part 45 of the first valve member 44 is approximately inparallel to the central axis of the exhaust gas passage 41. Under thefirst state of the first valve member 44 where the outer peripheral part45 of the first valve member 44 is in contact with the inner wall 46 ofthe exhaust gas pipe 26, a part of the exhaust gas passage 41 at theengine main system 13 side observed from the rotary shaft 42 is closed.

On the other hand, under the second state of the first valve member 44where the first valve member 44 becomes in parallel to the exhaust gasflow, namely, is positioned approximately in parallel to the centralaxis of the exhaust gas passage 41, the exhaust gas passage 41 is fullyopened, namely, is not closed by the first valve member 44.

The second valve member 47 and the other rotary shaft 43 are assembledtogether. The second valve member 47 rotates around the rotary shaft 43.The first valve member 44 and the second valve member 47 areindependently driven by the control unit 17.

The second valve member 47 rotates from a first state to a second state,where in the first state, the outer peripheral part 48 of the secondvalve member 47 is closed to the inner wall 46 of the exhaust gas pipe26 around the rotary shaft 43. In the second state, the outer peripheralpart 48 of the second valve member 47 is approximately in parallel tothe central axis of the exhaust gas passage 41. Under the first state ofthe second valve member 47 where the outer peripheral part 48 of thesecond valve member 47 is closed to the inner wall 46 of the exhaust gaspipe 26, the exhaust gas flows into the outside of the three waycatalyst unit 32 in the diameter direction of the exhaust gas pipe 26,namely, the upper stream side in FIG. 1A, through between the inner wall46 of the exhaust gas pipe 26 and the outer peripheral part 48 of thesecond valve member 47. In this state, the second valve member 47becomes in a semi-opening condition to open a part of the exhaust gaspassage 41.

On the other hand, under the second state of the second valve member 47where the outer peripheral part 48 of the second valve member 47 isapproximately in parallel to the central axis of the exhaust gas passage41, the second valve member 47 makes a fully opening condition not toclose any part of the exhaust gas passage 41.

The throttle unit 40 has a drive unit 49 (or a throttle drive meansshown in FIG. 1B) for driving the first valve member 44 and the secondvalve member 47.

The drive unit 49 is comprised of an electric motor, for example. Thiselectric motor receives a control signal as an instruction transferredfrom the control unit 17, and controls the opening condition (namely,between the semi-opening state and the fully opening state) of the firstvalve member 44 and the second valve member 47 based on the receivedcontrol signals.

The first valve member 44 and the second valve member 47 are drivenindependently of each other. That is, the opening state of the firstvalve member 44 is controlled independently of the opening state of thesecond valve member 47.

FIG. 3A to FIG. 3C, each shows the opening state of the throttle unit(or the valve) assembled in the exhaust gas purifying apparatusaccording to the first embodiment of the present invention.

As shown in FIG. 3A, when the first valve member 44 is in thesemi-opening state and the second valve member 47 is also in thesemi-opening state, the opening state of the throttle unit 40, namely,the inclination of the throttle unit 40 to the central axis of theexhaust gas passage 41 decreases the gas-flow sectional area of theexhaust gas passage 41.

At this time, the first valve member 44 and the second valve member 47guide the exhaust gas flowing in the exhaust gas passage 41 toward theouter peripheral side in the diameter direction of the three waycatalyst unit 32.

The exhaust gas is thereby introduced into a part of the outer end partof the three way catalyst unit 32 in the diameter direction.

As shown in FIG. 3B, when the first valve member 44 is in thesemi-opening state, and on the other hand, the second valve member 47 isin the fully opening state, the throttle unit 40 decreases the gas-flowsectional area of the exhaust gas passage 41, but increases the gas-flowsectional area rather than that of the state shown in FIG. 3A where boththe first valve member 44 and the second valve member 47 are in thesemi-opening state.

In this case, the first valve member 44 and the second valve member 47guide the exhaust gas flowing in the exhaust gas passage 41 into theupper half area of the three way catalyst unit 32. That is, the exhaustgas is introduced into the upper half area of the three way catalystunit 32.

Still further, as shown in FIG. 3C, when the first valve member 44 andthe second valve member 47 are in the fully opening state, the throttleunit 40 does not decrease the gas-flow sectional area of the exhaust gaspassage 41. The exhaust gas flowing through the exhaust gas passage 41is introduced into the three way catalyst unit 32 along the exhaust gaspassage 41 without being obstructed by the first valve member 44 and thesecond valve member 47. The exhaust gas is therefore introduced into theentire of the three way catalyst unit 32.

Next, a description will now be given of the operation of the exhaustgas purifying apparatus 12 having the above structure with reference toFIG. 4. FIG. 4 is a flow chart of the operation flow of the exhaust gaspurifying apparatus according to the first embodiment of the presentinvention.

When an ignition switch is turned on (step S101), the operation flowgoes to step S102. The control unit 17 judges whether or not thegasoline engine 11 is in its starting operation (step S102). By the way,the ignition switch is omitted from the drawings.

When the judgment result in step S102 indicates that the gasoline engine11 is not in the starting operation, the operation flow goes to stepS103. In step S103, the control unit 17 judges whether or not thegasoline engine 11 is now rotating. That is, the control unit 17 judgeswhether the gasoline engine 11 is in the starting operation which is inan early period of starting the gasoline engine 11, namely, within apredetermined period of time counted from the start of the gasolineengine 11, or the gasoline engine 11 is in a normal operation which hasbeen adequately elapsed after the predetermined period of time has beenelapsed after the gasoline engine 11 starts.

When the judgment result in step S103 indicates that the gasoline engine11 is not rotating, namely, the gasoline engine 11 is not in the normaloperation condition, the control unit 17 completes the routine shown inFIG. 4. When the judgment result in step S103 indicates that thegasoline engine 11 is not rotating, the gasoline engine 11 is not in thenormal operation although the ignition switch is turned on. Accordingly,this condition indicates that the gasoline engine 11 is not operatingand no exhaust gas is emitted from the engine main system 13. Thecontrol unit 17 therefore completes the routine shown in FIG. 4.

When the judgment results in step S102 and step S103 indicate that thegasoline engine 11 is in the start operation and the gasoline engine 11is now rotating, the operation flow goes to step S104. In step S104, thecontrol unit 17 judges whether or not the temperature of the three waycatalyst placed in the three way catalyst unit 32 is lower than apredetermined temperature “t”, where the control unit 17 obtains thetemperature of the three way catalyst based on a detection signaltransferred from the temperature sensor 33.

The predetermined temperature “t” which the control unit 17 uses whenthe above judgment regarding the temperature of the three way catalystis an activation temperature of the three way catalyst in the three waycatalyst unit 32, for example. That is, the control unit 17 judges instep S104 whether or not the temperature of the three way catalyst islower than its activation temperature. By the way, when the temperatureof the three way catalyst in the three way catalyst unit 32 is detectedbased on the temperature of the exhaust gas which flows in the exhaustgas passage 41, it is acceptable that the predetermined temperature “t”has a different value of the activation temperature of the three waycatalyst in the three way catalyst unit 32. In this case, thepredetermined temperature “t” is set in advance based on a relationshipbetween the temperature of the three way catalyst unit 32 and thetemperature of the exhaust gas.

The judgment result in step S104 indicates that the temperature of thethree way catalyst in the three way catalyst unit 32 is lower than thepredetermined temperature “t”, the control unit 17 instructs the firstvalve member 44 to close (step S105). The control unit 17 then generatesand transfers the drive signal to the drive unit 49 in order to drivethe first valve member 44. The first valve member 44 is thereby drivenso that the outer peripheral part 45 of the first valve member 44 is incontact with the inner wall 46 of the exhaust gas pipe 26 around therotary shaft 42. As a result, as shown in FIG. 3A, the exhaust gaspassage 41 is entered into the semi-opening state where a part of thecross section of exhaust gas passage 41 in the exhaust gas pipe 26 isclosed by the first valve member 44.

The control unit 17 drives the first valve member 44 (step S105), andfurther adjusts the opening ratio of the second valve member 47 in theexhaust gas pipe 26 (step S106).

The control unit 17 outputs the drive signal to the drive unit 49 inorder to drive the second valve member 47. The control unit 17determines the opening ratio of the second valve member 47 according tothe temperature of the three way catalyst unit 32 detected in step S104.

For example, when the temperature of the three way catalyst unit 32 isadequately lower than its activation temperature during the period, likethe state immediately after the engine main system 13 starts, as shownin FIG. 3A, the control unit 17 instructs the drive unit 49 to rotatethe second valve member 47 so that the outer peripheral part 48 of thesecond valve member 47 is closed to the inner wall 46 of the exhaust gaspipe 26.

On the other hand, the control unit 17 controls the second valve member47 so that the second valve member 47 rotates from the position shown inFIG. 3A to the position shown in FIG. 3B based on increasing thetemperature of the three way catalyst unit 32. In particular, FIG. 3Ashows the position of the second valve member 47, in which the outerperipheral part 48 of the second valve member 47 is closed at the innerwall 46 of the exhaust gas pipe 26. FIG. 3B shows the position of thesecond valve member 47, in which the outer peripheral part 48 of thesecond valve member 47 reaches the central axis of the exhaust gaspassage 41 in the exhaust gas pipe 26.

That is, according to the temperature rise of the three way catalyst inthe three way catalyst unit 32, the outer peripheral part 48 of thesecond valve member 47 is moved from the inner wall 46 side to thecentral axis of the exhaust gas passage 41. As a result, the gas-flowsectional area of the exhaust gas passage 41 is switched from the stateshown in FIG. 3A to the state shown in FIG. 3B. The state shown in FIG.3A indicates the semi-opening state in which the exhaust gas isintroduced into a part of the outer periphery of the three way catalystunit 32. The state shown in FIG. 3B indicates the half-opening state inwhich the exhaust gas is introduced into the upper half of the three waycatalyst unit 32.

As described above, according to the exhaust gas purifying apparatus ofthe first embodiment, through the drive unit 49 the control unit 17controls the first valve member 44 to close the lower half area of theexhaust gas passage 41 shown in FIG. 3A, and further controls the secondvalve member 47 to close a large part of the exhaust gas passage 41shown in FIG. 3A.

The exhaust gas flowing in the exhaust gas passage 41 is therebyintroduced into a part of the outer periphery of, namely, the upper endpart of the three way catalyst unit 32 shown in FIG. 3A. According toincreasing the temperature of the three way catalyst unit 32, thecontrol unit 17 drives the second valve member 47 to increase thegas-flow sectional area of the exhaust gas passage 41, without drivingthe first valve member 44. That is, the first valve member 44 maintainsthe state to close the lower half part of the exhaust gas passage 41. Itis thereby possible to gradually increase the gas-flow sectional area ofthe exhaust gas passage 41 by shifting the outer peripheral part 48 ofthe second valve member 47 from the inner wall 26 side to the centralaxis side of the exhaust gas passage 41 in the exhaust gas pipe 26. As aresult, the exhaust gas flowing in the exhaust gas passage 41 isintroduced into the three way catalyst in the three way catalyst unit 32from a part of the upper side to the upper half of the three waycatalyst unit 32 according to rotating the second valve member 47.

When the judgment result in step S104 indicates that the temperature ofthe three way catalyst unit 32 is not less than the predeterminedtemperature “t”, namely, than its activation temperature, the controlunit 17 instructs the drive unit 49 to drive the first valve member 44and the second valve member 47 to be fully opened (step S109). Thecontrol unit 17 outputs the drive signal to the drive unit 49 in orderto drive the first valve member 44. The second valve member 47 ispositioned on the central axis of the exhaust gas passage 41 because ofthe temperature rise of the catalyst in the three way catalyst unit 32.The control unit 17 instructs the drive unit 49 to move the first valvemember 44 onto the central axis of the exhaust gas passage 41. Thiscontrol of the control unit 17 makes the state in which the first valvemember 44 and the second valve member 47 are positioned on the centralaxis of the exhaust gas passage 41. As a result, the exhaust gas passage41 enters the fully-opened state in which the exhaust gas passage 41 isnot closed by the first valve member 44 and the second valve member 47.This makes it possible to introduce of the exhaust gas in the exhaustgas passage 41 into the three way catalyst in the three way catalystunit 32 without any obstacles

After adjusting the opening condition of the first valve member 44 andthe second valve member 47 in step S105, step S106, or step S109according to the temperature of the three way catalyst unit 32, thecontrol unit 17 instructs the injector 21 in the engine main system 13to inject the gasoline as fuel into the combustion chamber 22 (stepS107). Thus, the control unit 17 transfers the drive signal to theinjector 21 in order to inject the fuel. When the injector 21 injectsthe fuel into the combustion chamber 22, the control unit 17 instructsan ignition plug (not shown, or a spark plug) to ignite the fuel in thecombustion chamber 22 (step S108).

As described above in detail, the exhaust gas purifying apparatus of thefirst embodiment has the throttle unit 40 comprised of the first valvemember 44 and the second valve member 47. The throttle unit 40 controlsthe opening state of the first valve member 44 and the second valvemember 47 so as to adjust the gas-flow sectional area of the exhaust gaspassage 41 and to control the amount of the exhaust gas flowing in theexhaust gas passage 41. In particular, when the temperature of the threeway catalyst unit 32 is low, the throttle unit 40 introduces the exhaustgas into a part of the outer periphery side of the three way catalystunit 32. The throttle unit 40 gradually increases the gas-flow sectionalarea of the exhaust gas passage 41 according to the temperature rise ofthree way catalyst unit 32. When the temperature of the three waycatalyst unit 32 reaches its activation temperature, the throttle unit40 fully opens the gas-flow sectional area of the exhaust gas passage41. That is, the control unit 17 instructs the drive unit 49 to fullyopen both the first valve member 44 and the second valve member 47 inthe exhaust gas passage 41.

FIG. 5A is a diagram showing a relationship between the temperature ofthe three way catalyst unit 32 and the elapsed period of time countedfrom the start or re-start of the gasoline engine in the engine mainsystem 13 shown in FIG. 2. FIG. 5B is a diagram showing a relationshipbetween the elapsed period of time counted from the start of thegasoline engine and a concentration of hydro carbon (HC) contained inthe exhaust gas emitted from the engine main system 13, one which isequipped with the exhaust gas purifying apparatus according to the firstembodiment of the present invention and the other, as a comparisonexample, is equipped with a conventional exhaust gas purifyingapparatus.

According to the exhaust gas purifying apparatus of the firstembodiment, the exhaust gas is introduced into a part of the three waycatalyst unit 32 when the temperature of the three way catalyst in thethree way catalyst unit 32 is low. As a result, as shown in FIG. 5A,when compared with the conventional exhaust gas apparatus which isequipped with no throttle unit 40, the temperature of the three waycatalyst in the three way catalyst unit 32 in the exhaust gas purifyingapparatus rapidly rises after the engine main system 13 starts. When thetemperature of the three way catalyst of the three way catalyst unit 32reaches the activation temperature, the control unit 17 controls thethrottle unit 40 so as to fully open the exhaust gas passage 41, so thatthe exhaust gas is introduced into the entire of the three way catalystunit 32. This control decreases the pressure loss of the exhaust gas inthe exhaust gas passage 41. The exhaust gas purifying apparatusaccording to the first embodiment of the present invention provides thefunction to rapidly rise the temperature of the three way catalyst inthe three way catalyst unit 32, and also provides the pressure loss ofthe exhaust gas without increasing the size of the exhaust gas purifyingapparatus. Still further, as shown in FIG. 5B, when compared with theconventional exhaust gas purifying apparatus equipped with no throttleunit, the structure of the exhaust gas purifying apparatus of the firstembodiment can decrease the concentration of hydro carbon (HC) containedin the exhaust gas passing through the exhaust gas purifying apparatuseven though the gasoline engine in the engine main system 13 is in theinitial stage to start.

Second Embodiment

A description will be given of the exhaust gas purifying apparatusaccording to the second embodiment of the present invention withreference to FIG. 6.

FIG. 6 is a schematic cross section of a part of the exhaust gaspurifying apparatus according to the second embodiment of the presentinvention. As shown in FIG. 6, the exhaust gas purifying apparatus 12 ofthe second embodiment has a throttle unit 50 instead of the throttleunit 40 according to the first embodiment. The throttle unit 50 of thesecond embodiment has a pair of the throttle valve members 51 and a pairof valve drive units 52. Each throttle valve member 51 is a plate shape.One end of each throttle valve member 51 is rotatably fixed to the innerwall of the exhaust gas pipe 26. That is, each exhaust gas pipe 26rotates around a rotary shaft 53. As shown in FIG. 6, each throttlevalve member 51 has a movable end part 54 which is extended toward thethree way catalyst unit 32 side. According to the rotation of thethrottle valve member 51 around the rotary shaft 53, the movable endpart 54 moves from the inner side toward the outer side in the diameterof the three way catalyst unit 32.

The valve drive unit 52 rotatably drives the throttle valve member 51around the rotary shaft 53. The valve drive units 52 serve as the valvedrive means which is used in the claims according to the presentinvention.

As shown in FIG. 6, when the movable end part 54 of the throttle valvemember 51 is positioned at the inner side in the diameter direction ofthe three way catalyst unit 32, the sectional area of the exhaust gaspassage 41 is more decreased according to approaching the three waycatalyst unit 32.

When the movable end part 54 of the throttle valve member 51 ispositioned at the inner side in the diameter direction of the three waycatalyst unit 32, the exhaust gas in the exhaust gas passage 41 isintroduced into the central part in the diameter direction of the threeway catalyst unit 32.

On the other hand, when the movable end part 54 of the throttle valvemember 51 is positioned at the outer side in the diameter direction ofthe three way catalyst unit 32, the movable end part 54 is positioned atthe inner wall 46 side of the exhaust gas pipe 26 in which the three waycatalyst unit 32 is placed. In this case, the gas-flow sectional area ofthe exhaust gas passage 41 is more increased according to approachingthe three way catalyst unit 32, and the exhaust gas in the exhaust gaspassage 41 is introduced into the entire of the three way catalyst unit32.

In the structure of the exhaust gas purifying apparatus according to thesecond embodiment of the present invention, the temperature sensor 33 isplaced at the upstream side of the throttle unit 50, as shown in FIG. 6,namely, placed at the engine main system 13 side.

When receiving the detection signal transferred from the temperaturesensor 33, the control unit 17 estimates the temperature of the threeway catalyst in the three way catalyst unit 32 based on the temperatureof the exhaust gas flowing in the exhaust gas passage 41 at the upstreamside of the throttle unit 50. It is possible to have a structure inwhich the temperature sensor 33 directly detects the temperature of thethree way catalyst in the three way catalyst unit 32, like the structureof the first embodiment.

In the structure of the exhaust gas purifying apparatus according to thesecond embodiment of the present invention, when the temperature of thethree way catalyst in the three way catalyst unit 32 is low, the controlunit 17 controls the valve drive unit 52 to move the movable end part 54of the throttle valve member 51 toward the central part of the three waycatalyst unit 32. The exhaust gas flowing in the exhaust gas passage 41is introduced into a part of the central part of the three way catalystunit 32 in the diameter direction of the three way catalyst unit 32.According to the temperature rise of the three way catalyst unit 32, thecontrol unit 17 controls the valve drive unit 52 to drive the movableend part 54 of the throttle valve member 51 toward the outer part of thethree way catalyst unit 32 in its diameter direction. Therefore thesectional area of the three way catalyst unit 32 to introduce theexhaust gas is increased according to the temperature rise of the threeway catalyst unit 32.

In the structure of the exhaust gas purifying apparatus according to thesecond embodiment of the present invention, when the temperature of thethree way catalyst in the three way catalyst unit 32 is low, the exhaustgas is introduced into the central part of the three way catalyst unit32 by the throttle valve member 51. The central part of the three waycatalyst unit 32 is heated by the introduced exhaust gas. This promotesa partial heating of the three way catalyst in the three way catalystunit 32. As a result, specified materials such as HC, CO, and NOxcontained in the exhaust gas are oxidized or reduced at the central partof the three way catalyst unit 32. Introducing the exhaust gas into thecentral part of the three way catalyst in the three way catalyst unit 32decreases the amount of thermal discharge from the outer peripheral wallof the exhaust gas pipe 26. For example, the exhaust gas pipe 26 is madeof stainless steel having a relatively high thermal conductivity. On theother hand, the three way catalyst unit 32 is supported in a filter madeof ceramics. In general, ceramics have a low thermal conductivity. Forthis reason, the central part of the three way catalyst unit 32 has ahigh heat insulating capability when compared with the outer peripheralpart thereof. As a result, the exhaust gas introduced into the three waycatalyst unit 32 rapidly heats the three way catalyst in the three waycatalyst unit 32. Accordingly, it is hard to decrease the temperature atthe central part of the three way catalyst unit 32. This provides therapid increase of the temperature of the three way catalyst in the threeway catalyst unit 32 to its activation temperature. This enables thespecified materials such as HC, CO, and NOx contained in the exhaust gasto be eliminated. The specified materials are generally contained in theexhaust gas from early period of starting the gasoline engine 11 in theengine main system 13.

The throttle valve member 51 moves toward the inner wall 46 side of theexhaust gas pipe 26 according to increasing the temperature of the threeway catalyst unit 32 in order to expand the gas-flow sectional area ofthe exhaust gas passage 41. The exhaust gas flowing in the exhaust gaspassage 41 is introduced into the entire part of the three way catalystunit 32 when the temperature of the three way catalyst unit 32 reachesits activation temperature. This can decrease the pressure loss of theexhaust gas, like the structure of the exhaust gas purifying apparatusaccording to the first embodiment.

Third Embodiment

A description will be given of the exhaust gas purifying apparatusaccording to the third embodiment of the present invention withreference to FIG. 7.

FIG. 7 is a schematic cross section of a part of the exhaust gaspurifying apparatus according to the third embodiment of the presentinvention. As shown in FIG. 7, the exhaust gas purifying apparatus ofthe third embodiment has a throttle unit 60 instead of the throttleunits 40 and 50 of the first and second embodiments.

The throttle unit 60 has a pair of throttle valve members 61. Eachthrottle valve member 61 has a bimetal 62. The bimetal 62 drives thecorresponding throttle valve member 61. The bimetal 62 is deformedaccording to the temperature change of the exhaust gas. That is, thedeformation of the bimetal 62 drives a movable end part 64 of thethrottle valve member 61 from the central part toward the outer part ofthe three way catalyst unit 32. That is, the bimetal 62 serves as avalve drive member which will be used in the claims according to thepresent invention.

The throttle valve member 61 is driven by the bimetal 62. Thetemperature of the three way catalyst unit 32 correlates with thetemperature of the exhaust gas. That is, the temperature of the threeway catalyst of the three way catalyst unit 32 is low when thetemperature of the exhaust gas is low in early period of starting theengine main system 13. On the other hand, the temperature of the threeway catalyst of the three way catalyst unit 32 and the temperature ofthe exhaust gas become high when the engine main system 13 is stablyoperating.

Because of deforming the bimetal 62 according to the temperature changeof the exhaust gas, the movable end part 64 of the throttle valve member61 is positioned at the central part side of the three way catalyst unit32 when the temperature of the exhaust gas is low, and positioned at theouter peripheral side of the three way catalyst unit 32 when thetemperature of the exhaust gas is high.

In the structure of the exhaust gas purifying apparatus of the thirdembodiment, the temperature sensor 33 is placed at the upstream side (orat the gasoline engine side) of the throttle unit 60, like the structureof the second embodiment. It is also possible to have another structurein which the temperature sensor is placed in the three way catalyst unit32 in order to directly detect the temperature of the three way catalystunit 32.

In the structure of the third embodiment, the deformation of the bimetal62 drives the throttle valve member 61. The structure of the thirdembodiment can eliminate the power source to drive the throttle valvemember 61 such as a throttle valve drive unit.

Fourth Embodiment

A description will be given of the exhaust gas purifying apparatusaccording to the fourth embodiment of the present invention withreference to FIG. 8.

FIG. 8 is a schematic cross section of a part of the exhaust gaspurifying apparatus according to the fourth embodiment of the presentinvention. As shown in FIG. 8, the exhaust gas purifying apparatus ofthe fourth embodiment has a throttle unit 70 instead of the throttleunits 40, 50, 60 of the first to third embodiments. As shown in FIG. 8,the throttle unit 70 has a pair of elastic members 72. Each elasticmember 72 supports a corresponding throttle valve member 71. The elasticmember 72 is made of a spring, for example. One end of the elasticmember 72 is fixed to the throttle valve member 71, and the other end ofthe elastic member 72 is connected to the inner wall of the exhaust gaspipe 26. The elastic member 72 gently presses the throttle valve member71 to the inner wall of the exhaust gas pipe 26. One end of the throttlevalve member 71 is fixed to the exhaust gas pipe 26 through a rotaryshaft 73. The throttle valve member 71 rotates around the rotary shaft73.

When the amount of the exhaust gas flowing in the exhaust gas passage 41is low, a movable end part 74 of the throttle valve member 71 ispositioned at the central side of the three way catalyst unit 32 by thepressing force of the elastic member 72. Because the pressing force ofthe elastic member 72 is relatively small, the movable end part 74 ofthe throttle valve member 71 is moved from the central side toward theouter peripheral side of the three way catalyst unit 32 when the amountof the exhaust gas flowing in the exhaust gas passage 41 is increased.That is, the elastic member 72 serves as the valve drive means which isused in the claims according to the present invention.

The amount of the exhaust gas is changed according to the load of theengine main system 13. The more the load of the engine main system 13increases, the more the amount of the exhaust gas increases. Inaddition, the more the load of the engine main system 13 increases, themore the temperature of the exhaust gas rises. As a result, the more theload of the engine main system 13 increases, the more the temperature ofthe three way catalyst in the three way catalyst unit 32 rises. That is,the flow rate of the exhaust gas correlates with the temperature of thethree way catalyst in the three way catalyst unit 32. Accordingly, whenthe gas flow rate of the exhaust gas is low, the temperature of thethree way catalyst unit 32 is also low.

In the structure of the exhaust gas purifying apparatus of the fourthembodiment, the temperature sensor 33 is placed at the upstream side ofthe throttle unit 70, like the structure of the second embodiment. It isacceptable to place the temperature sensor 33 to the three way catalystunit 32 in order to directly detect the temperature of the three waycatalyst unit 32.

In the structure of the exhaust gas purifying apparatus of the fourthembodiment, when the gas flow rate of the exhaust gas is low, namely,when the temperature of the three way catalyst in the three way catalystunit 32 is low, the movable end part 74 of the throttle valve member 71in the throttle unit 70 is moved toward the central side of the threeway catalyst unit 32.

When the temperature of the three way catalyst unit 32 is low, theexhaust gas is introduced into the central part of the three waycatalyst unit 32 by the throttle unit 70. According to increasing theflow rate of the exhaust gas, the movable end part 74 of the throttlevalve member 71 is gradually moved from the central side toward theouter peripheral side of the three way catalyst unit 32. This operationof the movable end part 74 of the throttle valve member 71 expands thegas-flow sectional area in the exhaust gas passage 41. Thus, thestructure of the exhaust gas purifying apparatus of the fourthembodiment changes the gas-flow sectional area in the exhaust gaspassage 41 according to the gas flow rate of the exhaust gas withoutusing any power source to drive the throttle unit 70 such as a valvedrive unit. The adjustment of the gas-flow sectional area of the exhaustgas passage 41 can promote heating of the central part of the three waycatalyst unit 32 when the gas flow rate of the exhaust gas in theexhaust gas passage 41 is low.

Fifth Embodiment

A description will be given of the exhaust gas purifying apparatusaccording to the fifth embodiment of the present invention withreference to FIG. 9.

FIG. 9 is a schematic cross section of a part of the exhaust gaspurifying apparatus according to the fifth embodiment of the presentinvention. As shown in FIG. 9, a throttle unit 80 is placed, at thedownstream side of the three way catalyst unit 32, in the flow directionof the exhaust gas in the exhaust gas passage 41. Closing a part of thegas-flow sectional area in the exhaust gas passage 41 by the throttleunit 80 generates a pressure difference in the gas-flow sectional areaof the exhaust gas passage 41. This pressure difference allows theexhaust gas to mainly flow the part of the three way catalyst unit 32,which is not closed by the throttle unit 80. Thus, the structure of theexhaust gas purifying apparatus of the fifth embodiment, in which thethrottle unit 80 is placed at the downstream side of the three waycatalyst unit 32, controls the flow of the exhaust gas in the three waycatalyst unit 32.

In the structure of the exhaust gas purifying apparatus of the fifthembodiment, the throttle unit 80 has a first valve member 81 and asecond valve member 82. The first valve member 81 and the second valvemember 82 are independently driven around rotary shafts 83 and 84.

When both the first valve member 81 and the second valve member 82 arepositioned at the central axis along the longitudinal direction of theexhaust gas passage 41, namely, positioned in parallel to the exhaustgas flow, the throttle unit 80 enters the fully opening state in whichboth the first valve member 81 and the second valve member 82 do notclose the gas-flow sectional area of the exhaust gas passage 41. In thatcase, the exhaust gas is introduced into the entire of the three waycatalyst unit 32.

It is so designed that the outer diameter of the first valve member 81is smaller than the inner diameter of the exhaust gas passage 41. Thisstructure forms a gas-flow passage between an end part 85 of the firstvalve member 81 and the inner wall 46 of the exhaust gas pipe 26 whenthe first valve member 81 is positioned to be approximatelyperpendicular to the central axis of the exhaust gas passage 41.

When both the first valve member 81 and the second valve member 82 arepositioned to be approximately perpendicular to the central axis of theexhaust gas passage 41, the exhaust gas flowing in the exhaust gaspassage 41 is introduced into a part of the outer peripheral side of thethree way catalyst unit 32, namely, into the upper side of the exhaustgas passage 41 shown in FIG. 9. As a result, this can promote heating ofthe outer peripheral part of the three way catalyst unit 32 throughwhich the exhaust gas mainly flows.

In the structure of the exhaust gas purifying apparatus of the fifthembodiment, as shown in FIG. 9, the temperature sensor is placed at thedownstream side of the throttle unit 80, namely, at the opposite side ofthe engine main system 13. The control unit 17 receives the detectionsignal transferred from the temperature sensor 33, and estimates thetemperature of the three way catalyst in the three way catalyst unit 32based on the received detection signal which indicates the temperatureof the exhaust gas flowing in the exhaust gas passage 41 at thedownstream side of the throttle unit 80.

It is also possible to have a structure in which the temperature sensor33 directly detects the temperature of the three way catalyst in thethree way catalyst unit 32, like the structure of the first embodiment.

The structure of the exhaust gas purifying apparatus of the fifthembodiment controls the gas-flow sectional area in the exhaust gaspassage 41 for the exhaust gas at the downstream side of the three waycatalyst unit 32. The structure of the exhaust gas purifying apparatusof the fifth embodiment enables the exhaust gas to be introduced intothe entire surface of the three way catalyst unit 32 at the upstreamside of the three way catalyst unit 32. Because the structure of thefifth embodiment increases the contact area of the exhaust gas with thethree way catalyst in the three way catalyst unit 32, it is possible toincrease the function to purify specified materials such as HC, CO, andNOx contained in the exhaust gas even if the flow rate of the exhaustgas is low.

Sixth Embodiment

A description will be given of the exhaust gas purifying apparatusaccording to the sixth embodiment of the present invention withreference to FIG. 10.

FIG. 10 is a schematic cross section of a part of the exhaust gaspurifying apparatus according to the sixth embodiment of the presentinvention. The structure of the sixth embodiment is a modification ofthe structure of the first embodiment.

As shown in FIG. 10, an exhaust gas heating unit 90 is placed at theupstream side of the three way catalyst unit 32 in the exhaust gaspurifying apparatus, namely, at the engine main system 13 side. Theexhaust gas heating unit 90 has an electrical heater unit or a burnerThe control unit 17 instructs the exhaust gas heating unit 90 to heatthe exhaust gas when the temperature of the three way catalyst unit 32is low. Thus, the exhaust gas heating unit 90 heats the exhaust gas tobe introduced into the three way catalyst in the three way catalyst unit32.

Thus, supplying the high-temperature exhaust gas heated by the exhaustgas heating unit 90 into the three way catalyst unit 32 can rapidlyincrease the temperature of the three way catalyst in the three waycatalyst unit 32. Because the exhaust gas purifying apparatus of thesixth embodiment has the exhaust gas heating unit 90 to directly heatthe exhaust gas in the exhaust gas passage 41, the exhaust gas heated bythe exhaust gas heating unit 90 is introduced into the three waycatalyst unit 32. Because this structure can provide rapidly increasingthe temperature of the three way catalyst in the three way catalyst unit32 from early period of starting the engine main system 13, it ispossible to purify specified materials such as HC, CO, and NOx containedin the exhaust gas from early period of starting the engine main system13.

In the structure of the exhaust gas purifying apparatus of the sixthembodiment, the exhaust gas heating unit 90 is added into the structureof the first embodiment. The present invention is not limited by thiscase, for example, it is possible to add the exhaust gas heating unit 90into each of the structure of the exhaust gas purifying apparatus ofeach of the second to fifth embodiments.

(Other Modifications)

The present invention is not limited by the structures of the exhaustgas purifying apparatus according to the first to sixth embodimentsdescribed before. For example, it is acceptable to place a plurality ofthe temperature sensors 33 at the upstream side and downstream sideobserved from the three way catalyst unit 32 along the exhaust gas flowin the exhaust gas passage 41 in the exhaust gas pipe 26. In thisstructure, the control unit 17 estimates the temperature of the threeway catalyst in the three way catalyst unit 32 based on the correlationbetween the temperature of each temperature sensor and the temperatureof the three way catalyst in the three way catalyst unit 32.

Features and Effects of the Present Invention

In the exhaust gas purifying apparatus as another aspect of the presentinvention, the throttle unit decreases a gas-flow sectional area of theexhaust gas passage in the exhaust gas pipe. The throttle unitintroduces the exhaust gas flowing in the exhaust gas passage into thepart of the catalyst. This structure enables the temperature of thecatalyst to rapidly rise within a short period of time counted from theinternal combustion engine start.

In the exhaust gas purifying apparatus as another aspect of the presentinvention, the throttle unit increases the gas-flow sectional area ofthe exhaust gas passage according to the temperature rise of thecatalyst detected by the catalyst temperature detection means. Thisstructure enables the catalyst to receive a large amount of the exhaustgas from the internal combustion engine according to the temperaturerise of the internal combustion engine after this engine starts orre-start, and the temperature rise of the catalyst. The exhaust gasadequately warms the catalyst until the temperature of the catalystreaches its activation temperature. Therefore it is not necessary tohave a large size of the catalyst unit for a large amount of thecatalyst in order to completely purify the exhaust gas. This structurecan decrease specified materials such as HC, CO, and NOx contained inthe exhaust gas emitted from the internal combustion engine withoutincreasing the pressure loss of the exhaust gas and also withoutincreasing the size of the exhaust gas purifying apparatus.

In the exhaust gas purifying apparatus as another aspect of the presentinvention, the throttle unit gradually increases the gas-flow crosssection of the exhaust gas passage from the outer peripheral side towardthe inner side of the catalyst unit along a diameter direction of thecatalyst unit according to the temperature rise of the catalyst in thecatalyst unit. Still further, the throttle unit has a rotary shaft, afirst valve member, a second valve member, a throttle drive means. Therotary shaft is placed in the diameter direction of the exhaust gaspassage in the exhaust gas pipe. The first valve member rotates aroundthe rotary shaft to open and close the exhaust gas passage at theupstream side of the rotary shaft in the upstream side of the catalystunit. The second valve member rotates around the rotary shaft to openand close the exhaust gas passage at the downstream side of the rotaryshaft in the upstream side of the catalyst unit. The throttle drivemeans independently drives the first valve member and the second valvemember. The above simple structure of the exhaust gas purifyingapparatus makes the exhaust gas flow in the outer peripheral side of thecatalyst in the diameter direction. Thus, it is possible to forcedlyintroduce the exhaust gas into the part of the catalyst with the simplestructure of thee exhaust gas purifying apparatus, and possible toincrease the temperature of the catalyst within a short period of timecounted from the internal combustion engine start.

In the exhaust gas purifying apparatus as another aspect of the presentinvention, the throttle unit expands the gas-flow sectional area of theexhaust gas passage from the central side toward the outer peripheralside in the diameter direction of the catalyst unit according toincreasing the temperature of the catalyst. Still further, the throttleunit has a throttle member and a valve drive means. The throttle memberexpands from the inner wall of the exhaust gas pipe toward the catalystunit side. The valve drive means drives the throttle member between thecentral side and the outer peripheral side in the diameter direction ofthe catalyst unit.

In the structure of the exhaust gas purifying apparatus, the throttleunit expands the gas-flow sectional area of the exhaust gas passage fromthe central side toward the outer peripheral side of the catalyst in thediameter direction of the catalyst unit according to the temperaturerise of the catalyst. That is, during the low temperature of thecatalyst, the throttle unit introduces the exhaust gas into the centralpart in the diameter direction of the catalyst unit. A large part of theexhaust gas is mainly supplied into the central part of the catalyst inthe catalyst unit. The heat energy of the exhaust gas is transmitted tothe central part of the catalyst. Therefore, it is difficult todischarge the heat energy of the central part of the catalyst toward theoutside of the catalyst unit through the outer peripheral side of thecatalyst unit. As a result, this structure of the exhaust gas purifyingapparatus according to the present invention promotes the temperaturerise of the catalyst. It is therefore possible to increase thetemperature of the catalyst within a short period of time counted fromthe re-start or start of the internal combustion engine.

The exhaust gas purifying apparatus as another aspect of the presentinvention, further has an exhaust gas heating means that is placed atthe upstream side of the catalyst unit in order to heat the exhaust gasbefore it reaches the catalyst unit. This exhaust gas heating meansheats the exhaust gas before the supply to the catalyst. The heatedexhaust gas flowing into the catalyst further promotes to increase thetemperature of the catalyst. Therefore it is possible to increase thetemperature of the catalyst within a short period of time counted fromthe internal combustion engine start.

While specific embodiments of the present invention have been describedin detail, it will be appreciated by those skilled in the art thatvarious modifications and alternatives to those details could bedeveloped in light of the overall teachings of the disclosure.Accordingly, the particular arrangements disclosed are meant to beillustrative only and not limited to the scope of the present inventionwhich is to be given the full breadth of the following claims and allequivalent thereof.

1. An exhaust gas purifying apparatus comprising: an exhaust gas pipethat forms an exhaust gas passage in which an exhaust gas emitted froman internal combustion engine flows; a catalyst unit having a catalystplaced in the exhaust gas passage; catalyst temperature detection meanscapable of detecting a temperature of the catalyst placed in thecatalyst unit; and a throttle unit, placed in at least one of anupstream side and an downstream side of the catalyst unit, capable ofintroducing the exhaust gas flowing in the exhaust gas passage into apart of the catalyst unit when the temperature of the catalyst detectedby the catalyst temperature detection means is lower than an activationtemperature of the catalyst.
 2. The exhaust gas purifying apparatusaccording to claim 1, wherein the throttle unit decreases a gas-flowsectional area of the exhaust gas passage in the exhaust gas pipe. 3.The exhaust gas purifying apparatus according to claim 2, wherein thethrottle unit increases the gas-flow sectional area of the exhaust gaspassage according to the temperature rise of the catalyst detected bythe catalyst temperature detection means.
 4. The exhaust gas purifyingapparatus according to claim 3, wherein the throttle unit graduallyincreases the gas-flow cross section of the exhaust gas passage from theouter peripheral side toward the inner side of the catalyst unit along adiameter direction of the catalyst unit according to the temperaturerise of the catalyst in the catalyst unit.
 5. The exhaust gas purifyingapparatus according to claim 4, wherein the throttle unit comprises: arotary shaft placed in the diameter direction of the exhaust gas passagein the exhaust gas pipe; a first valve member that rotates around therotary shaft to open and close the exhaust gas passage at the upstreamside of the rotary shaft in the upstream side of the catalyst unit; asecond valve member that rotates around the rotary shaft to open andclose the exhaust gas passage at the downstream side of the rotary shaftin the upstream side of the catalyst unit; and a throttle drive meansthat independently drives the first valve member and the second valvemember.
 6. The exhaust gas purifying apparatus according to claim 3,wherein the throttle unit expands the gas-flow sectional area of theexhaust gas passage from the central side toward the outer peripheralside in the diameter direction of the catalyst unit according to thetemperature rise of the catalyst.
 7. The exhaust gas purifying apparatusaccording to claim 6, wherein the throttle unit comprises: a throttlemember that expands from the inner wall of the exhaust gas pipe towardthe catalyst unit side; and a valve drive means that drives the throttlemember between the central side and the outer peripheral side in thediameter direction of the catalyst unit.
 8. The exhaust gas purifyingapparatus according to claim 1, further comprising an exhaust gasheating means that is placed at the upstream side of the catalyst unitin order to heat the exhaust gas before it reaches the catalyst unit. 9.The exhaust gas purifying apparatus according to claim 1, furthercomprising a control means capable of controlling the operation of thethrottle unit, wherein the control means is an electronic control unitcomposed a microcomputer that comprises a central control unit, a readonly memory, and a random access memory.
 10. The exhaust gas purifyingapparatus according to claim 1, wherein the catalyst is a three waycatalyst placed in the catalyst unit.